Estimation of global recoverable human and animal faecal biomass

Human and animal faeces present persistent threats to global public health and also opportunities for recovery of resources. We present the first global-scale accounting of recoverable faeces (livestock animal and human) from 2003 to 2030 using country-specific human and animal population estimates and estimated species-specific faeces production by human or animal body mass. We also examine global coverage of domestic livestock animals and sanitation facilities to describe the distribution of onsite versus offsite hazards from animal and human faeces. In 2014, the total mass of faeces was 3.9 x 10(12)kg per year, increasing by >52 x 10(9)kg per year since 2003 and anticipated to reach at least 4.6 x 10(12)kg in 2030. Annual global production of faeces from animals (primarily cattle, chickens and sheep) was about four times that from humans. Ratios of animal faeces to human faeces continue to increase (geometric mean of 4.2:1 for 2003 versus 5.0:1 for 2014 versus a projected 6.0:1 for 2030). Low-income populations bear the greatest burden of onsite faeces, mostly from animals in or near the domestic environment. This analysis highlights the challenges of resource recovery from concentrated and dispersed sources of faeces, and the global public health policy needed for safe management of animal faeces.